The invention relates to a mixing and kneading machine comprising an elongated casing having a material inlet and a material outlet, a first shaft and a second shaft rotatably mounted in said casing for rotational movement for moving a material from said inlet to said outlet, said first shaft and said second shaft being provided with means for rotating said first shaft at a faster speed than said second shaft. Kneading members are provided on the shafts and engage one another in toothed wheel-like manner and have an angle of inclination bringing about an axial feed and at least the kneading members of the more rapidly driven shaft are spacedly juxtaposed in the longitudinal direction of the shaft.
A machine of this type is, for example, known from Swiss Pat. No. 506,322. The kneading members of the second shaft therein have the function of cleaning the main shaft and its disk-shaped kneading members because, particularly when performing thermal reactions in the machines, the product tends to adhere to the surfaces. In order to bring about an improved mixing and kneading action, it is advantageous for both shafts to be driven at different speeds, so that there is a greater product movement in one part of the machine and a product exchange with the other part of the machine. However, as the kneading arms have an angle of inclination in the case of continuous product passage bring about a faster product feed in that part of the machine enclosing the more rapidly driven shaft, there is a non-uniform residence time distribution of the product within the machine.
The kneading members of this known machine have kneading arms extending parallel to the casing wall and in the longitudinal direction of the casing, so that they have a roughly bow-shaped configuration. Particularly when treating pasty or doughy product, it is frequently the case that the product also adheres to the kneading arms and moves therewith, without undergoing further mixing or kneading. Product already adhering to the arms causes further product to adhere thereto, so that the product closes the kneading member space enclosed by the bow shape.